1. Field of the Invention
The present invention relates to a measuring system and a screening method for the thermal conductive efficiencies of thermal conductive devices. In particular, the present invention is to rapidly measure the thermal conductive efficiencies of thermal conductive devices (for example, heat pipes, heat spreaders, heat sinks, etc.) so as to attain the object of screening the thermal conductive efficiencies of the thermal conductive devices, and thus can greatly reduce manpower and time cost and meet the requirements of stable reproducibility, resolution and reliability.
2. Description of the Related Art
With the trends of micro-miniaturization and multi-function of electronic products, it will bring devices and systems significant influences. Since more transistors need to be contained in a limited space and more heat thus increased to vary the work functions of the electronic devices, this will cause an extremely challenge to engineers in this area. A current traditional system heat dissipating solution mode leads heat generated by a high heat-generating device, such as CPU or VGA, into a heat sink or a metal block having a high thermal conductive property through a packaging surface layer and conducts the heat to a heat exhausting device (for example, a fan, a heat sink, etc.) through a thermal conductive device, (for example, a heat pipe, a heat spreader, etc.), so that the high-heat-generating device can operate at a constant operation temperature. It is a design concept for a basic heat dissipating module.
When a chip trends to micro-miniaturization and function integration, if heat generated per unit area can be rapidly spreaded to the whole substrate through a high thermal conductive heat pipe so as to uniformly spread and conduct the heat to heat sinks which contact with the chip and to minimize the non-stability of the device caused by local hot points, the reliability and lifetime of the device can be efficiently enhanced.
Since inner operating fluid of the heat pipe absorbs heat by the phase change between liquid and gas phases and transmits heat by gas molecules, the heat pipe can obtain a much higher thermal conductivity and has a quite good thermal conductive effect. Therefore, in the module, heat generated by a high heat-generating device, such as CPU/GPU and so on, is rapidly transmitted in the phase change inside the heat pipe, a better heat exchange way is provided by more protruding heat sinks, the heat is exhausted out to the air by a fan. The heat generated by the CPU/GPU can be took away at one time and the operating temperature is greatly reduced, it means that its heat dissipating efficiency is obviously. Therefore, how to rapidly and effectively ensure the efficiency of the heat pipe by a measuring method is a main issue which needs to be studied.
A measuring method for a traditional thermal conductive device (for example, a heat pipe) generally applies heat generated by inputting a constant power to the heating terminal of the heat pipe. When the heating terminal reaches a set temperature T1 (for example, 70° C.), a cooling device (typically, a fan or a water jacket) at a heat dissipating terminal is activated. Whether the thermal conductive capability of the heat pipe reaches the requirement of the input constant power value is judged based on if the temperature of the heating terminal can be cooled down and the temperature difference ΔT between the heating terminal (T1) and the heat dissipating terminal (T2).
Such measuring method only obtains a thermal conductive efficiency of the heat pipe at a specific heating power each time. Each measurement takes about 3 to 5 minutes. If it is required to measure the maximum thermal conductive capability (Qmax), the input power of the heating terminal must be gradually increased until the temperature of the heating terminal cannot be cooled down. At this time, the highest power value measured in the previous measurement is defined as the maximum thermal conductive capability (Qmax) of the heat pipe. The measurements from the low power to the high power typically require 5 or 6 times to obtain the Qmax value. That is, it takes 15 to 30 minutes or more in average to measure the Qmax of one heat pipe. So, it is quite time consuming.
The above-stated traditional measuring method still has a vague point on the cooling method for the cooling terminal. In general, a fan or a water jacket is frequently used to cool the cooling terminal. As for how to decide the air flow of the fan or the water flow and temperature of the water jacket, it does not be clearly defined in measurements. It merely states that its flow rate which can cool the heating terminal. Therefore, it is frequently found in practice that when the heating terminal reaches the set temperature T1, immediate after the heat dissipating module for the cooling terminal is activated, if the flow rate is too large at the first time, it may cause a dry out effect to the heat pipe; however, if the flow rate is slowly increased, the heat pipe does not have the dry out effect and can cool down the temperature of the heating terminal. From the above, it is obvious that the control of the flow rate will affect the result of the measurement. If it is required to obtain a precise. Qmax value, the control of the flow rate becomes quite important since the thermal conductive capability of one heat pipe is constant at the same operation condition. However, this part does not be strictly defined on current measurement standard. In other words, not only the traditional measuring method consumes more manpower and time cost, but also the reproducibility, resolution and reliability of the measurements are unstable, so its application value is low.